Calling circuit



Feb. 21, 1933. H. B. ARNOLD ET AL CALLING C IRCUIT Filed April 17, 1930QQEQQQSE Q Q m.

QM Km QMQEUQ M 3+ Q Q IIHI' g Q HB. ARA/01.0 wvavrag: LIB. cooks 7% 6%aZ ATTORNEY Patented Feb. 21, 1933 UNITED STATES PATENT OFFICE HEN RY B.ARNOLD ANID LEIGI-I'ION B. COOKE, OF NEW YORK, N. Y., ASSIGNORS TO WEST-ERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK; N. Y., A CORPORATION01? CF:

NEW YORK CALLING CIRCUIT Application filed April 17, 1930. Serial No.445,077.

This invention relates to communication systems and particularly tocalling circuits for power line carrier-current telephone systerms.

5 One objectof the invention is to provide a communication system thatshall effect selective calling between stations by calling circuitsunder the control of a telephone dial switch having pulsing contactswhich may be initially either in a closed or open position.

Another object of the invention is to provide a power-linecarriercurrent system effecting communication in both directions bymodulated currents within the same frequency band that shall haveselective calling circuits under the control of a telephone dialswitch'having pulsing contacts which may be initially either in a closedor open position.

A further object of the invention is to provide a power linecarrier-current system that shall effectselective calling betweenstations by a code signal preceded by a prolonged calling impulse andthat shall have the calling circuits controlled during transmission ofthe code signal by a telephone dial switch having pulsing contacts whichmay be initially either in a closed or open position.

In a power line carrier-current telephone system it is desirable tolimit the frequency range of the modulated currents employed to a narrowrange by reason of the transmission characteristics of the power line.In the communication'system disclosedin the a patent to C. N. Nebel#1,733,553 dated October 29, 1929, communication in both direc tions iseffected bymeans of modulated currents within the same frequency range.In 40 the present invention which is applied to a system of the typedisclosed in the Nobel patent, calling between stations is efiected bycarrier-current modulated with impulses of voice frequency current andwithin the same 5 frequency range as the currents employed tocommunicate between stations. V7 hen carrier-current modulated withimpulses of voice frequency current is employed for call ing purposes,means must be employed to prevent operation of the calling selectors atthe signal stations by means of the communication currents.

In the present invention the calling of a distant station is effected bya signal comprisinga prolonged impulse followed by a code signal ofcarrier-current modulated with impulses of voice frequency current. Thesystem disclosed in the above mentioned Nebel patent is employed todisclose the present invention. The calling impulses employed forcalling purposes are modulated and demodulated in the manner disclosedin the Nebel patent. At the calling station an oscillator having afrequency within the voice frequency range is controlled by a pulsingrelay in accordance with the calling signal to be transmitted. Normallywhen the pulsing relay is released, the calling oscillator is connectedto the transmitting channel of the associated signal station. {79

The pulsing relay is controlled by a telephone dial switch and theenergization of the calling oscillator is controlled by the telephoneswitchhook. Upon the removal of the removal of the receiver from theswitchhook at said station.

The telephone dial switch, which controls the pulsing relayto transmitacalling code signal over the power line, has the cam member thereofmodified in order to transmit a small number of impulses but ofrelatively longer duration. The cam member, which operates in thecustomary manner, opens and closes a pair of pulsing contacts at halfthe speed of the usual operation of such contact members in telephonedial switches. Moreover, the pulsing contact members are left in theposition last moved to by the cam mem- 95 ber. Thus the pulsing contactmembers may be either in closed or open condition when it is desired totransmit a calling signal. Means comprising an off-normal relay and acontrol relay are provided under the control 1 of the pulsing contactsand the off-normal contacts of the dial switch for governing the pulsingrelay to transmit a calling code signal over the power line and fordisconnecting the calling oscillator from the power line upon completionof a calling signal. The offnormal relay and the control relay insurethe operation of the pulsing relay in accordance with the operation ofthe dial switch irrespective of whether the pulsing contacts of the dialswitch are initially in the closed or open position.

The circuits for operating the calling selector at a called station arevery similar to the circuits disclosed in the application of L. B.Cooke, Serial No. 443,639, filed April 12, 1930. t the called station arelay has the contact members thereof in circuit with two slow operatingrelays. The slow operating relays are controlled by the prolongedimpulse preceding a calling code signal so that the relay connected tothe slow operating relays may operate a selector magnet through hecontact members of the slow operating relays when the code signalfollowing the prolonged impulse is received. Upon the operation of thecalling selector at the called station means is provided for insuringthe removal of the calling oscillator at such station from the powerline.

The single figure in the accompanying drawing is a diagrammatic view ofa signaling system constructed in accordance with the invention.

Referring to the drawing a signal station having a transmitting channel1 and a receiving channel 2 is connected to a power line comprisingconductors 3, 4 and 5 by means of a coupling filter 6. The couplingfilter may be of any simple type and preferably similar to the couplingfilter disclosed in the above mentioned patent to Nebel. Thetransmitting channel 1 is provided with two modulators 7 and 8 and thereceiving channel is provided with two demodulators 9 and 10. Themodulators in the transmitting channel and the demodulators in thereceiving channel are similar in construction and operation to likeparts disclosed in the before-mentioned patent to Nebel.

An operators telephone set comprising a receiver 11 and a transmitter 12is connected to the transmitting channel 1 and the receiving channel 2by means of a suitable hybrid coil 13. The switchhook of the operatorsset controls an auxiliary switch 14 for governing the calling circuitsin a manner to be described hereinafter. A calling oscillator 15 whichis preferably of the thermionic type produces a current having afrequency within the voice frequency range and is normally connectedacross the transmitting channel 1. The connection of the oscillator 15to the transmitting channel is controlled by means of a pulsing relay16. The pulsing relay 16 is provided with two switch members 17 and 18and two operating coils 19 and 20.

A modified telephone dial switch 21 is provided for controlling theoperation of an olfnormal relay 22 and a control relay 23 to govern theoperation of the pulsing relay 16. The dial switch 21 is provided withthe usual pulsing contacts 24 and ofi -normal contacts 25. The pulsingcontacts 24 in place of being controlled by the customary figure 8 cammember, are controlled by a cam member 26 shown in the drawing. The cammember 26 is operated in the customary manner and opens and closes thepulsing contact at half the speed of the usual operation of the pulsingcontacts by the figure 8 cam member.

The selectors provided in the system are operated by an odd number ofimpulses and preferably 17 impulses are required in the code signal. Onthe 17th impulse it will be noted that the cam member 26 would be in aposition opposite to the position from which it started. Accordingly,the pulsing contacts may be left either in an open or closed position atcompletion of the calling signal. Inasmuch as the oscillator 15 mustalways be removed from the transmitting channel during conversationbetween stations special means must be provided for insuring the removalof the oscillator from the transmitting channel at the completion of acalling signal irrespective of the position of the pulsing contacts.Moreover, means must be provided to insure the transmission of a correctcode signal irrespective of the initial position of the pulsingcontacts. The oilnormal relay 22 and the control relay 23 in sure thecorrect operation of the pulsing relay 16 in a manner to be hereinafterdescribed. The off-normal relay 22 is provided with two coils 2'? and 2Sand two switch members 29 and 30. The control relay 28 is provided withtwo coils 31 and 32 and three switch members 33, 34 and 35.

The receiving channel 2 is connected by a transformer 36 to a suitablerectifier 37 which in turn is connected to a receiving relay 38.

The receiving relay controls the operat-ion of two slow relays 39 and 40and a selector magnet 41. Selector magnet 41 operates a selector 42which controls a relay 43. The selector 42 is of the type disclosed inthe patent to J. C. Field #1343256 dated June 15, 1920. The relay 43 isprovided with a switch member 44 for completing a circuit from a battery45 to the calling bell 46 and a switch member 47 for establishing aholding circuit from a battery 48 to the coil of the relay. The relay 48is also provided. with a switch member 49 for completing a circuit froma battery 50 through a coil of relay 51.

Assuming the dial switch 21 to be in the position shown on the drawingwith the pulsing contacts 24 in an open position and it is desired toselectively call a distant station, the receiver 11 is first removedfrom the switchhook. Upon removal of the receiver from the switchhookthe switch 14 is operated for completing the circuit from the battery 59to operate a filament relay 56. The filament relay '56 completes acircuit from a battery 48 for energizing the oscillator 15. Theoscillator 15 is normally connected across the transmitting channel 1 bymeans of the switch member 18 of the pulsing relay 16. Carrier currentis modulated with the prolonged impulse from the oscillator 15 by meansof the modulators 7 and 8 in the manner described in the above mentionedpatent to Nobel. Thus an initial prolonged impulse is transmitted overthe power line to the distant called station.

Upon operation of the dial switch 21, the off-normal contacts 25complete a circuit from the battery 59 for operating the 011- normalrelay 22. The circuit completed by the off-normal contact may be tracedfrom battery 59 through the switch 14, elf-normal contacts 25, coil 27of the ofi-normal relay 22, switch member 33 of the control relay 23 andground return to the battery 59. Upon operation of the olf-n'ormal relay22 a circuit is completed for directly operating the pulsing relay 16 inaccordance with the opening and closing of the pulsing contacts 24. Theoperating circuit for the pulsing relay may be traced from the battery59 through the switch 14, pulsing contacts 24, switch member 30 of theo'li-normal relay 22, coil 20 of the pulsing relay 16 and ground returnto the battery 59. The switch member 18 of the pulsing relay controlsthe connection of the oscillator 15 to the transmitting channel 1 inaccordance with the code signal to be transmitted to the distantstation. Switch member 17 completes a circuit from battery 61 throughthe selector magnet at the calling station to operate the selector atthe calling station in accordance with the code signal beingtransmitted. Upon transmission of the 17th pulsingimpulse, which is thefinal impulse, the pulsing contacts 24 are closed to operate the pulsingrelay 16 and insure the removal or the oscillator 15 from thetransmitting channel 1 as is necessary when conversation talres place.

At the distant station, the prolonged impulse and the code signaltransmitted by the dial switch are demodulated by the demodulators 9 and10 and then rectified by the rectifier 37 for operating the receivingrelay 38. The prolonged impulse operates the relay 38 a suflicient timeto efiect operation or" the slow relays 40 and 39. The slow relays 39and 40 complete a circuit for permitting the operation of the selectormagnet 41 by the receivin relay 38 according to the received codesignal. The selector 42 is operated by the selector magnet 41 forcompleting a circuit from the battery 48 for operating the relay 43.Upon operation of the relay 43, the switch member 47 establishes aholding circuit, the switch member 44 completes a circuit for operatingthe bell 46 and the switch member 49 completes the circuit for operatingthe relay 51. The relay-51 is provided with a switch member 65 forcompleting the circuit from a battery 66 to effect operation of thepulsing relay 16 and insure disconnecting the oscillator 15 at thecalled station from the transmitting channel 1. The relay 51 is alsoprovided with a switch member 67 for establishing a holding circuit forthe. relay upon removal of the receiver from the switchhook at thecalled station.

Upon removal of the receiver from the switchhook at the called station,-a circuit is completed by the switch 14 for operating the filament relay56 to break the holding circuit established through the relay 43. Therelay 43 is released to stop operation of the calling bell 46. The relay51 which controls the circuit through the coil 19 of the pulsing relay16 is not released at this time by reason of the holding circuitestablished through the switch member 67. The various relays arereturned to normal position upon return of the receiver to theswitchhook at both the calling and called stations. At the callingstation the return of the receiver to the switchhook breaks the holdingcircuit which had been established through the coil 28 of the off-normalrelay 22. At the called station the return of the receiver to theswitchhook breaks the holding circuit established through the relay 51.

If the pulsing contacts of the dial switch 21 are initially in closedposition, the removal of the receiver 11 from the switchhook at thecalling station will complete a circuit for operating the control relay23. The circuit completed upon removal of the receiverfrom theswitchhook may be traced from the battery 59 through the switch 14,pulsing contacts 24, coil 31 of the control relay 23, switch member 29and ground return to the battery 59. The relay 23 is operated and ashunt circuit is established across the coil 20 of the pulsing relay 16to prevent operation of the relay 16 until the pulsing contacts 24 ofthe dial switch are open. The shunt circuit across the coil 20 may betraced from one terminal of the coil through the switch member 34,pulsing contacts 24, and switch member 35 to the other terminal of thecoil 20. Upon separation of the pulsing contacts 24 in accordance withthe code signal to be transmitted, a circuit is completed from thebattery 59 for energizing the coil 20 of the pulsing relay 16. Ontransmission of the 17th impulse, the pulsing contacts are opened toinsure operation of the pulsing relay 16 and the disconnection of theoscillator 15 from the transmitting channel.

Inasmuch as the same signal is transmitted over the power line to thecalled station when the pulsing contacts are initially in closedposition as when the pulsing contacts are initially in open positionthere is no difference in the operation at the called station inoperating the selector. Upon the completion of conversation between thestations, the replacing of the receiver on the switchhook at the callingstation serves to break the holding circuit which had been establishedfrom the battery 59 through the coil 32 of the control relay 23. It mabe noticed in the opera tion last described that the oil normal contactsof the dial switch perform no useful function.

Modifications in the system and in the arrangement and location of partsmay be made within the spirit and scope of the invention and suchmodifications are intended to be covered by the appended claims.

lVhat is claimed is:

1. In combination, a power line having telephone signal stationsconnected thereto, an oscillator, a pulsing relay for controlling theconnection of said oscillator to said line circuit, a dial switch havingpulsing contacts initially in open or closed position upon start of theswitch operation and off-normal contacts, an oil-normal relay operatedby said off-normal contacts who the dial switch starts operating withthe pulsing contacts in open position, means for locking said oanormalrelay under control of the receiver switchhook when operated by theoft-normal contacts, and means controlled by the off-normal relay whenenergized for operating the pulsing relay according to the operation ofsaid pulsing contacts.

2. In combination, a transmission circuit, an oscillator, a pulsingrelay for controlling the connection of'said oscillator to said circuit,a dial switch having pulsing contacts initially in open or closedposition upon start of the switch operation, a control relay operatedupon removal of the receiver from the switchhook when the pulsingcontacts are initially closed, means under control of the receiverswitchhook for locking the control relay when operated with the pulsingcontacts initially in closed position, and means comprising said controlrelay for operating the pulsing relay according to the operation of thepulsing contacts upon operation of the dial switch with the pulsingcontacts in closed position at the start of the switch operation.

3. In combination, an oscillator initially connected to a transmissioncircuit, a pulsing relay for interrupting the connection of saidoscillator to the circuit, a dial switch having pulsing contacts in openor closed position upon start of the switch operation and oilnormalcontacts, said pulsing contacts being opened and closed by alternatedial steps, an

oft-normal relay operated by said off-normal contacts when the dialswitch starts opera tion with the pulsing contacts in open position,means under control of the receiver switchhoolr for holding theoff-normal relay in operative position, means controlled by theoil-normal relay when energized for operating the pulsing relayaccording to the operation of said pulsing contacts, a control relayoperated upon removal of the receiver from the switchhook when thepulsing contacts of the dial switch are initially in closed position,and means comprising said control relay for operating the pulsing relayaccording to the operation of the pulsing contacts upon operation of thedial switch with the pulsing contacts in closed position at the start ofthe switch operation.

4-. In combination, a transmission line, an oscillator for transmittingsignals over said line, means comprising a pulsing relay for connectingsaid oscillator to said transmission line, a dial switch having pulsingcontacts initially in an open or closed position and so constructed thatthe pulsing contacts are either opened or closed only by each dial stepso that the pulsing contacts are opened during one step of the switchand held open until closed by the next succeeding step, and meanscontrolled by said dial switch irrespective of the starting position ofthe pulsing contacts for operating said pulsing relay to transmit a codesignal of impulses from said oscillator and for disconnecting saidoscillator from the transmission line upon completion of the codesignal.

5. In combination, a transmission line, an oscillator for transmittingsignals over said line, means comprising a pulsing relay for connectingsaid oscillator to the transmission line, a dial switch having pulsingcontacts initially in an open or closed position and so constructed thatthe pulsing contacts are either opened or closed only by each dial stepso that the pulsing contacts are opened dur-' ing one step of the switchand held open until closed by the next succeeding step, and meanscomprising an oil-normal relay operated when the pulsing contacts areinitially open and control relay operated when the pulsing contacts areinitially closed and cooperating with said dial switch irrespective ofthe starting position of the pulsing contacts for operating said pulsingrelay to transmit a code signal of impulses from said oscilla-' tor andfor disconnecting said oscillator from the transmission line uponcompletion of the code signal.

6. In a signal system, a power line having a plurality of signalstations connected thereto, an oscillator at a cal ing station having afrequency within the voice frequency range and initially connected tothe power line, means comprising a pulsing relay for controlling theconnection of said oscillator to the power line, means for energizingsaid oscillator upon removal of the receiver from the .switchhook at thecalling station, a dial switch at a calling station having pulsingcontacts which initially may be in an open or closed position, saidpulsing contacts being opened and closed by alternate dial steps, andmeans controlled by said dial switch irrespective of the startingposition of the pulsing contacts for varying the connection of saidoscillator to the power line according to a code signal of an odd numberof impulses and for disconnecting said oscillator from the power lineupon completion of the signal.

7. In a signal system, a power line having a plurality of signalstations connected thereto, an oscillator at a calling station, meansfor energizing said oscillator upon removal of the receiver from theswitchhoolr at the calling station and for connecting the oscillator tothe power line to transmit a prolonged impulse to the called station, adial switch at the calling station having pulsing contacts initially inan open or closed position and means controlled by the dial switchirrespective of the .starting position of the pulsing contacts forconnecting said oscillator to the power line to transmit a code signalof calling impulses to a called station.

8. In a signal system, a power line having a plurality of signalstations connected thereto, means for communicating between stations bymodulated currents within one frequency band, an oscillator at a callingstation having a frequency within the voice frequency range, modulatingmeans connected to the power line, a dial switch having pulsing contacts initially in open or closed position and so constructed that thepulsing contacts are either opened or closed only by each dial step sothat the pulsing contacts are opened during one step of the switch andheld open until closed by the next succeeding step, and means operatedby the dial switch irrespective of the initial position of the pulsingcontacts for connecting said oscillator to said modulating means inaccordance with a code signal to transmit a calling signal over thepower line. 7

9. In a signal system, a power line having a plurality of signalstations connected thereto, an oscillator at a calling station having afrequency within the voice frequency range and initially connected tothe power line, means comprising a pulsing relay for selectivelycontrolling the connection of said oscillator to the power line, meansfor energizing said oscillator upon removal of the receiver from theswitchhook at the calling station to transmit a prolonged callingimpulse to the called station, a dial switch at the calling stationhaving pulsing contacts initially in an open or closed position andmeans controlled by the dial switch irrespective of the startingposition of the pulsing contacts for operating the pulsing relay totransmit a code signal of calling impulses over the power line.

10. In a signal system, a power line having a plurality of signalstations connected thereto, an oscillator'at a calling station having afrequency within the voice frequency range and initially connected tothe power line, a dial switch at a calling station having pulsingcontacts which may be normally in an open or closed position, a pulsingrelay for controlling the connection of said oscillator to the powerline, means operated upon removal of the receiver from the switchhook atthe calling station for energizing said oscillator and for preparingcircuits to be completed by the dial pulsing and off-normal contacts,and means controlled by said dial switch irrespective of the startingposition of the pulsing contacts thereof for operating said pulsingrelay to transmit a code signal of impulses from said oscillator.

11. In a signal system, a power line having a plurality of signalstations connected thereto, calling oscillators at said stations eachhaving a frequency within the voice frequency range for transmittingcalling signals to the power line, modulating means connected to thepower line at said stations for modulating carrier current with voicefrequency currents, a pulsing relay at a calling station for selectivelyconnecting the calling oscillator to the modulating means at thestation, means for energizing the calling oscillator at the callingstation upon removal of the receiver from the switchhook to transmit aprolonged calling impulse to the power line, a dial switch at a callingstation having pulsing contacts initially in an open or closed position,and means controlled by the dial switch irrespective of the startingpostion of the pulsing contacts for operating the pulsing relay totransmit a code signal of calling impulses over the power line.

In witness whereof, we hereunto subscribe our names this 16th day ofApril, 1980. Y HENRY B. ARNOLD.

LEIGHTON B. COOKIE.

